This application claims the priority of Japanese application No. 9-284853, filed Oct. 17, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to an apparatus and a method of controlling an internal combustion engine, wherein a valve opening timing and a valve closing timing of an intake valve, and an exhaust valve of the internal combustion engine are controlled in accordance with an operation condition of the internal combustion engine.
As conventional methods of controlling a load of an internal combustion engine, one of them is a method for supplying a fuel amount suited to an air amount by controlling an intake amount according to a load and another of them is a method for controlling a fuel amount according to a load without a limitation of an intake amount. The above stated differences result from the property of the fuel to be used, namely the former method corresponds to a gasoline internal combustion engine and the latter method corresponds to a diesel internal combustion engine.
In general, the reason why the diesel engine has a good fuel consumption is that the intake amount is not squeezed and a pumping loss is not generated. On the other hand, in the gasoline engine because a load control is performed according to the intake amount, during a low load condition since it is necessary to squeeze the air amount, a throttle valve is provided on a midway of an intake air passage.
Accordingly, a pressure in an intake port which is provided a downstream of the throttle valve has a pressure lower than atmospheric pressure and has a negative pressure. Since a pressure in a combustion chamber at the end of an exhaust process has roughly atmospheric pressure, at the start of an intake process it presents negative pressure upstream of an intake valve (a side of the intake port) but it presents atmospheric pressure at the downstream (a side of the combustion chamber).
With the above stated reasons, so as to flow the air from the intake port side to the combustion chamber side, it is necessary to intake the air in accordance with a descent movement of a piston, then the engine requires the role of a working for taking in the air. This working is a negative working against the engine, accordingly it is called a pumping loss. In particular, during a low load condition and a middle load condition, since an opening degree of the throttle valve is small and the pumping loss is always generated, accordingly a bad fuel consumption condition results.
As a technique for reducing the pumping loss, a lean burn system has been proposed, in which to the same fuel amount by increasing the air amount the combustion is performed, and this lean burn system has been put to practical use. However, in this lean burn system, the air amount is controlled in accordance with the throttle valve and the pumping loss is generated at a considerable operation area.
To reduce the generation of the pumping loss to a minimum, it has been proposed that the air amount must be controlled at a vicinity of the combustion chamber and such a control must be carried out by the intake valve. By controlling a valve opening period and a valve lift amount of the intake valve the air amount can be. A minute control of the air amount necessary for an idling time is, however, adversely affected largely with regard to the accuracy for the valve opening period control and the valve lift amount control of the intake valve.